U.S. Pat. No. 5,225,747 describes a rotational angle detection device that measures the momentary angular position of a rotary hinge and supplies the measured data to a control unit. The rotational angle is detected by a potentiometer that is affixed substantially laterally adjacent to the rotary hinge in a sealed housing. By arranging the potentiometer coaxial to the rotational axis, the connection of the linkage arms is possible only with increased complexity due to the coaxial shaft of the potentiometer. By laterally arranging the potentiometer adjacent to the rotary hinge, additional installation space is required, whereby the design possibilities for arranging the movable parts of the convertible top mechanism are restricted.